We propose to resolve and purify to homogeneity the near 20 proteins which make up the replication machinery of E. coli. The physical and functional properties of these proteins will be defined by using the small phage chromosomes as template probes. A complete, step-by-step, molecular description of the entire replicative life cycle of these phage DNAs should go a long way toward clarifying the mechanisms of fork movement of the replicating chromosome. With regard to the initiation (and termination) of a cycle of E. coli chromosome replication, the origin (oriC) will be identified, transferred to a high-copy-number plasmid and its functional features explored in enzymatic studies of replication of that hybrid plasmid. Progress in this direction may reveal some facts about the fine regulatory chemistry which governs the growth of cells, integration of chromosomal duplication and cell division, and factors which distort orderly growth to premature cessation or uncontrolled proliferation. Enzymologic, genetic and physicochemical methods will be applied to gain these chemical insights into one of the most basic biologic processes.